class_docstr: This class is intended to represent a set of inter-subject regions
  It should inherit from some abstract multiple ROI class,
  not implemented yet.
docstr: returns the average of the coordinates for each region
          
docstr_tok: ["returns","the","average","of","the","coordinates","for","each","region"]
code: def centers(self):
      """returns the average of the coordinates for each region"""
      pos = self.position
      centers_ = np.array([np.mean(pos[k], 0) for k in range(self.k)])
      return centers_
  
file_path: nipy/nipy/labs/spatial_models/structural_bfls.py
imports: import numpy
  from scipy import stats
label_desc: Use image node_id 2 for calling the LandmarkRegions obj's underlying member method code with example usage: obj.centers() and returns: centers_